A Mauser C96 fitted with and without the optional shoulder stock by Michael Collins (Liam Neeson) in the 1916 Easter Rising scenes in the beginning. Two IRA assassins also uses the weapon to kill two respective police inspectors.
British officers, RIC Detectives and many IRA members including Michael Collins carry Webley Mk VIs throughout the film.
Webley Mk IV
Kitty Kiernan (Julia Roberts) pulls a Webley Mk IV on a potential assassin during the political rally scene. A second (probable) Webley IV is wielded by an assassin in the killings. Since the Mk. IV and V are so alike it's difficult to properly identify which model is used in some scenes.
Browning 1900
Both the Irish and British uses the Browning Model 1900. Vinny Byrne (Tom Murphy) uses a Model 1900 to shoot a British detective through a newspaper. A British detective is carrying one at his untimely death at the hands of a IRA assassin. Joe O'Reilly (Ian Hart) also uses one throughout the film.
Steyr 1912
Harry Boland (Aidan Quinn) uses a Steyr 1912 during the Civil War scenes in Dublin. It is also used by an IRA assassin in the Bloody Sunday scene.
Colt 1911
A Colt 1911 is used by Liam Tobin in the Bloody Sunday scene. Harry Boland takes one from an overzealous bodyguard during his confrontation with Collins.
Luger P08
The Luger P08 is carried exclusively by IRA soldiers/assassins who uses it to good effect on the British Military and Police prescense.
Luger P08 Artillery model
An IRA assassin is seen preparing for the strike on British/Irish intelligence officers with a Luger P08 Artillery model. It is identifiable via it's longer barrel and rear sight. The P08 "Marine" model had the long barrel but not the rear sight which also helps identify it as a Artillery model.
Rifles
Ross Mk.III
An IRA soldier can be seen surrendering a Ross Mk.III rifle in the Easter Rising scene.
Short Magazine Lee-Enfield (SMLE) Mk.I
IRA soldiers can be seen carrying Lee-Enfield Mk.I rifles during the Easter Rising scene and the Civil War fighting in Dublin.The Mk.I makes several apperances but for the most part the shots are fuzzy due to the quick pace of the scenes and it is difficult getting a clear/sharp screenshot of it.
Short Magazine Lee-Enfield (SMLE) MK.III
British and Irish forces throughout the film use Mk.III rifles.
Mauser Gewehr 98
The Mauser Gewehr 1898 is seen at least twice in the movie. Once during the urban fighting in the Civil War and later an IRA soldier (Jonathan Rhys Meyers) uses a Gewehr 1898 at the end of the film.
A Bergmann MP18 is used by IRA members to assassinate three British secret service agents in a cafe.
M1921 Thompson
IRA members are seen using the M1921 Thompson submachine guns following Bloody Sunday and during the civil war fighting in Dublin. This is historically accurate, as the IRA bought some of the first Thompson guns off the production line.
The movie version is the M1921A which lacks the compensator of the later M1921AC.
Heavy Weapons
Lewis Gun
The Lewis Gun is used by the Black And Tans, most noticeably to fire at Dublin tenements. Joe O'Reilly (Ian Hart) uses one mounted on an Irish Army troop truck.
Hotchkiss Mk.I
A pair of Hotchkiss Mk.I machine guns turret mounted on the British (and later Irish) armored car and is seen used in the Bloody Sunday scene.
Browning Automatic Rifle M1918
The Browning Automatic Rifle is seen in the hands of a Black and Tan and with an IRA member during the Civil War fighting in Dublin.
Vickers Gun
The British Vickers Machine Gun with a smooth water jacket is seen mounted on British and Irish vehicles. It is also seen at a checkpoint.
Lanz Mortar
Anti-treaty IRA forces are seen firing German WW1-era 91mm Lanz trench mortar Minenwerfer, during the street fighting in Dublin.
Ordnance QF 18 Pdr
Used by the British army during the Easter Rising, and the Irish Army during the Civil War